Nonlinear finite-element analysis of the role of dynamic changes in blood perfusion and optical properties in laser coagulation of tissue

A nonlinear finite-element program was developed to simulate the dynamic evolution of coagulation in tissue considering temperature and damage dependence of both the optical properties and blood perfusion rate. These dynamic parameters were derived based on the Arrhenius rate process formulation of thermal damage and kinetics of vasodilation. Using this nonlinear model, we found that the region of increased blood flow that formed at the periphery of the coagulation region significantly reduces the heat penetration. Moreover, increased scattering in the near-surface region prevents light penetration into the deeper region. Therefore, if the dynamic parameters are ignored, a relatively significant overestimation of the temperature rise occurs in a deeper area resulting in an overestimation in predicted depth of coagulation. Mathematical modeling techniques that simulate laser coagulation may not provide reliable information unless they take into account these dynamic parameters.